U.S. patent number 5,863,620 [Application Number 08/545,816] was granted by the patent office on 1999-01-26 for process and apparatus for coating printed circuit boards.
This patent grant is currently assigned to Ciba-Geigy AG. Invention is credited to Hans-Jurgen Schafer.
United States Patent |
5,863,620 |
Schafer |
January 26, 1999 |
Process and apparatus for coating printed circuit boards
Abstract
A process for coating printed circuit boards with a coating
composition that is crosslinkable by electromagnetic radiation,
especially UV radiation, using the roll coating process, is
distinguished by the following process steps: a photopolymerisable,
meltable, low-molecular-weight coating composition that is highly
viscous to solid at room temperature and has an average molecular
weight of preferably from 500 to 1500 is melted and fed to the
applicator roll of a roll coating apparatus; the coating
composition is coated at a temperature of approximately from
60.degree. to 110.degree. C. and a viscosity of approximately from
1000 to 20000 mPas on to the surface(s) of a printed circuit board
in a thickness of approximately from 10 to 200 .mu.m, the surface
of the printed circuit board to be coated being pre-heated, prior
to coating, to a temperature that is approximately from 10.degree.
to 50.degree. C. higher than the application temperature of the
coating composition. An apparatus suitable for carrying out the
process outlined above is also described.
Inventors: |
Schafer; Hans-Jurgen (Viersen,
DE) |
Assignee: |
Ciba-Geigy AG (Basel,
CH)
|
Family
ID: |
27544671 |
Appl.
No.: |
08/545,816 |
Filed: |
December 29, 1995 |
PCT
Filed: |
May 10, 1994 |
PCT No.: |
PCT/IB94/00102 |
371
Date: |
December 29, 1995 |
102(e)
Date: |
December 29, 1995 |
PCT
Pub. No.: |
WO94/27190 |
PCT
Pub. Date: |
November 24, 1994 |
Foreign Application Priority Data
|
|
|
|
|
May 12, 1993 [DE] |
|
|
43 15 774.2 |
Jul 22, 1993 [DE] |
|
|
43 24 585.4 |
Sep 3, 1993 [DE] |
|
|
43 29 731.5 |
Sep 3, 1993 [DE] |
|
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43 29 730.7 |
Nov 8, 1993 [DE] |
|
|
43 37 907.9 |
Jan 24, 1994 [DE] |
|
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44 01 778.2 |
|
Current U.S.
Class: |
427/508; 118/263;
118/222; 118/202; 427/558; 427/553; 427/211; 118/262; 427/428.08;
427/96.9; 427/96.2; 427/97.6; 427/428.17 |
Current CPC
Class: |
G03F
7/16 (20130101); H05K 3/0091 (20130101); H05K
3/1216 (20130101); H05K 2203/159 (20130101); H05K
2203/111 (20130101); H05K 2203/0577 (20130101); H05K
3/227 (20130101); H05K 2203/1509 (20130101); H05K
2203/1572 (20130101); H05K 2203/1476 (20130101); H05K
2203/1366 (20130101); H05K 2203/0143 (20130101) |
Current International
Class: |
H05K
3/00 (20060101); G03F 7/16 (20060101); H05K
3/22 (20060101); H05K 3/12 (20060101); B05D
005/12 (); C08S 002/48 () |
Field of
Search: |
;427/96,97,211,428,508,553,557,558,314 ;118/202,262,263,222,66 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Research Disclosure, vol. 36, No. 024, Apr. 10, 1992, Emsworth, GB,
Anonymous "Printed Circuit Board Air Track Conveyor Incorporating
Heater and HEPA Filter". .
Research Disclosure, vol. 272, No. 023, Dec. 10, 1986, Emsworth,
GB, Anonymous, "Solder Mask Lamination". .
IBM Technical Disclosure Bulletin, vol. 30, No. 10, Mar. 1988, New
York, US, Anonymous, "Photoresist Adhesion to Dry-Plated Card/Board
by Controlled Thermal Method"..
|
Primary Examiner: Talbot; Brian K.
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
LLP
Claims
What is claimed is:
1. A process for coating printed circuit boards using a roll
coating process, wherein
a photopolymerizable, meltable coating composition that is viscous
to solid at room temperature and has an average molecular weight of
from 500 to 1500 is melted and fed to an applicator roll of said
roll coating process, and
the coating composition is coated at a temperature of approximately
from 60.degree. to 110.degree. C. and a viscosity of approximately
from 1000 to 20000 mPas onto the surface(s) of a printed circuit
board in a thickness of approximately from 10 to 200 .mu.m,
the surface of the printed circuit board to be coated being
pre-heated prior to coating.
2. A process according to claim 1, wherein the temperature of the
surface of the printed circuit board to be coated is adjusted to a
temperature of approximately 70.degree. to 160.degree. C. such that
it is approximately from 10.degree. to 50.degree. C. higher than
the application temperature of the coating composition.
3. A process according to claim 1, wherein the coating composition
is brought to the application temperature and the application
viscosity, by means of heatable applicator rolls, before it is
coated onto the surface(s) of the printed circuit board.
4. A process according to claim 1, wherein a through-gap between
applicator rolls of the roll coating apparatus is adjusted to
approximately from 50% to 95% of the thickness of the printed
circuit board.
5. A process according to claim 1, wherein a coating composition
having a softening range of approximately from 20.degree. to
80.degree. C. is used.
6. A process according to claim 1, wherein top and bottom surfaces
of the printed circuit boards are coated, the coating being carried
out simultaneously.
7. A process according to claim 1, wherein, after application and
before further processing, the coating is partially crosslinked by
a tempering step or brief exposure to UV radiation in order that
the printed circuit board has a non-tacky surface.
8. A process according to claim 1, wherein the coating produces a
solder mask.
9. A process according to claim 1, wherein the coating is used as a
mask for the production of solder deposits.
10. A process according to claim 1, wherein the coating produces an
etching or electro resist.
11. A process according to claim 1, wherein the coating produces a
permanent resist for additive processes.
12. A process according to claim 1, wherein the coating covers
rest-ring-free through-holes located on said printed circuit
board.
13. The process according to claim 1, wherein said applicator rolls
are rubberized or rubber coated.
14. An apparatus for coating printed circuit boards using a roll
coating apparatus having at least one applicator roll and devices
for applying the coating composition to applicator rolls, wherein
the roll coating apparatus is equipped with a melting vessel for a,
meltable photopolymerizable coating composition that is viscous to
solid at room temperature and has an average molecular weight of
from 500 to 1500, which melting vessel can be heated and the
temperature of which can be controlled to an application
temperature of approximately from 60.degree. to 110.degree. C. and
from which the melted coating composition is fed to the applicator
roll, and wherein there is provided a device for pre-heating the
surface of the printed circuit board that is to be coated, in which
device the surface of the printed circuit board is pre-heated prior
to coating.
15. An apparatus according to claim 14, wherein the roll coating
apparatus comprises at least one heatable applicator roll by means
of which the meltable coating composition can be brought to an
application viscosity of approximately from 1000 to 20000 mPas
before it is coated onto the surface of the printed circuit
board.
16. An apparatus according to claim 14, wherein devices for
applying the coating composition to the applicator rolls comprise
at least one metering roll, which is heatable and the temperature
of which can be adjusted to approximately from 70.degree. to
160.degree. C.
17. An apparatus according to claim 14, wherein the roll coating
apparatus is arranged for the simultaneous coating of both sides of
the printed circuit boards and comprises two heatable metering
rolls as well as two heatable applicator rolls, between which there
is left a through-gap of variable width that is approximately from
50% to 95% of the thickness of the printed circuit boards to be
coated.
18. An apparatus according to claim 14, wherein there is arranged
down-stream of the roll coating apparatus a tempering station or a
UV exposure station in which the coating of the printed circuit
board can be rendered non-tacky by tempering or by brief exposure
to UV radiation.
19. An apparatus according to claim 14, wherein said at least one
applicator roll is rubberized.
Description
BACKGROUND OF THE INVENTION
The invention relates to a process and apparatus for coating
printed circuit boards with a coating that is crosslinkable by
electromagnetic radiation, especially UV radiation
The function of the printed circuit board is to provide the
conductive connection to the components. As miniaturisation
progresses, the number of connections is becoming ever greater,
with the result not only that printed circuit board technology has
produced multilevel circuitry, but also that conductive tracks are
becoming ever narrower, drill hole diameters are becoming ever
smaller and the number of conductive tracks between two holes is
becoming ever greater.
With the development of surface-mounted devices it has been
possible to achieve a further reduction in the surface area
required. This has led to conductor widths of less than 100 .mu.m,
to drill hole diameters of from 0.3 to 0.2 mm and to solder point
diameters of only up to 0.4 mm with up to seven conductive tracks
between a drill hole grid of 2.54 mm. At the same time, more and
more connections must be made per integrated circuit, which results
in connection pad grids of from 0.3 to 0.4 mm. The problems
resulting from the increasingly high integration density are very
complex and require a comprehensive solution. They begin first with
the production of the conductive pattern.
For the production of a conductive pattern, the drilled copper-clad
base material is coated with a positive or negative resist. While
such resists were in the past screen-printable etching or electro
resists, nowadays photoresists are predominantly used, which are
solid or liquid resists. They are either laminated on to the
surface (solid resists) or applied by means of a pouring machine or
using rolls (liquid resists). After the application of a mask, the
conductive pattern is fixed, for example, by exposure to UV light,
with polymerisation of the resist, and exposed by development. This
leads to the so-called pattern plating process. In pattern plating,
first of all a mask is applied and only the conductor-free areas
are exposed and developed. The conductive tracks are then built up
by electroplating and the drilled contact holes are clad with
copper. After the conductors have been deposited by electroplating,
they are, for example, provided with a tin coating, the electro
resist is removed and the conductive pattern is etched. Since the
etching speed is the same in all directions, the undercutting
corresponds approximately to the thickness of the copper film used.
The undercutting that occurs in the etching stage of the pattern
plating process represents the limit for large-scale application of
that process. Moreover, the production of conductors of equal
height is frequently not possible as a result of the geometry of
the bath or of the printed circuit board.
Accordingly, for microconductor technology, the so-called panel
plating process was developed. In that process, starting with the
drilled copper-clad base material, first of all the surface of the
printed circuit board and the drilled holes are clad with copper by
electroplating in order to achieve a uniform thickness of the
copper layer. A dry film resist is then laminated on, exposure is
effected using a mask, and development is carried out.
In the case of microconductors, however, constrictions frequently
occur because the line pressure of the laminating roller is unable
to compensate for uneven areas of the base material, so that the
dry film resist does not adhere to the same extent in all places.
It is especially important that the already copper-clad drill holes
should also be protected from the effects of the etching. That is
achieved by covering the holes with resist, so-called
"tenting".
Further miniaturisation and the technology of surface-mounted
components has led to so-called "rest-ring"-free through-holes. Dry
film lamination technology cannot be used in this case, because
without the so-called rest-rings the resist film cannot be attached
to the surface of the printed circuit board. However, in order to
be able to cover also rest-ring-free holes with resist and thus
protect them from the effects of the etching, so-called
electro-immersion coating was found, which deposits a resist film
from 5 to 15 .mu.m thick from a coating bath in the hole and on the
surface of the printed circuit board. However, that process is very
cost-intensive and, because of the thinness of the coating, can be
used only together with the panel plating process.
WO 93/14444 proposes a hot coating process which is based on the
use of a meltable photoresist that is highly viscous at room
temperature, which photoresist, after liquefaction, is coated on to
cooled printed circuit boards using the curtain pouring process. As
the photomelt resist comes into contact with the cooled printed
circuit boards, it is cooled at the walls of the drill holes, so
that it is unable to run into the drill holes and forms over the
hole a covering supported at the wall of the hole. Although cooling
the printed circuit boards produces good results with printed
circuit boards that are still unstructured, the technique cannot be
used for cooled printed circuit boards. In that case, the
conductive tracks act as cooling fins. The photomelt resist cools
suddenly as it comes into contact with the conductive surface, as a
result of which air can become trapped between the conductive
tracks.
There are also known processes in which a coating composition is
coated on to printed circuit boards by means of steel rolls. The
simultaneous coating of both sides of the printed circuit boards in
a roll coating apparatus having two heated applicator rolls is
especially economical. For that purpose it is customary to use
surface-coating systems that contain a high proportion of solvent
and have a low viscosity. The surface tension must be low so that
the coating is able to spread easily without forming streaks. This
two-sided coating process requires the surfaces of the printed
circuit boards to be as even as possible. In the coating of printed
circuit boards that are already provided with conductive tracks,
constrictions may occur over the conductors, so that reliable
covering is not guaranteed. In addition, the hollow spaces that are
present as a result of undercutting beneath the edges of the
conductors are frequently not filled with coating, which leads to
defective areas after soldering and allows moisture to
penetrate.
Accordingly, the problem underlying the present invention is to
provide a coating process that permits the production of coatings
that are free of air bubbles. In particular, the process is to
permit the simultaneous coating of both sides of printed circuit
boards. It is also to be possible to coat printed circuit boards
having relatively high conductive tracks and at the same time
reliably to cover any through-plating holes that are present.
Undercuts at the edges of the conductors are to be filled
completely with coating. After drying, the surface of the coating
is to be substantially non-tacky and permit exposure using the
contact-exposure process. There is also to be provided an apparatus
that allows the process according to the invention to be carried
out.
SUMMARY OF THE INVENTION
All those problems and other associated problems are solved by a
process and an apparatus according to independent patent claims 1
and 13, respectively. Especially preferred variants of the process
according to the invention and of the associated apparatus
according to the invention are the subject of the corresponding
dependent process and apparatus claims, respectively. In
particular, the invention provides a process for coating printed
circuit boards with a coating composition that is crosslinkable by
electromagnetic radiation, especially UV radiation, using the roll
coating process, which process is distinguished by the following
process steps:
a photopolymerisable, meltable, low-molecular-weight coating
composition that is highly viscous to solid at room temperature and
has an average molecular weight of preferably from 500 to 1500 is
melted and fed to the applicator roll of a roll coating
apparatus;
the coating composition is coated at a temperature of approximately
from 60.degree. to 110.degree. C. and a viscosity of approximately
from 1000 to 20000 mPas on to the surface(s) of a printed circuit
board in a thickness of approximately from 10 to 200 .mu.m,
the surface of the printed circuit board to be coated being
pre-heated, prior to coating, to a temperature that is
approximately from 10.degree. to 50.degree. C. higher than the
application temperature of the coating composition.
The meltable coating composition is coated at a high viscosity of
from 1000 to 20000 mPas and under a high pressure, applied
preferably on both sides, by means of heated rubberised applicator
rolls having a temperature of from 60.degree. to 110.degree. C., to
heated printed circuit boards having a temperature that is from
10.degree. to 50.degree. C. higher than the temperature of the
applicator rolls. The high viscosity on the applicator roll
prevents the coating composition from being squeezed out over the
conductors. The high line pressure, which is preferably applied on
both sides, together with the decreasing viscosity of the coating
composition on the printed circuit board, ensures that all hollow
spaces beneath the conductors are filled completely. The coating
composition is liquefied even further on the hotter surface of the
printed circuit board and flows to the edges of the conductors,
thus covering them in the optimum manner.
The process according to the invention for coating printed circuit
boards with a meltable coating composition using a roll coating
apparatus eliminates the problems encountered hitherto, such as
coating composition being squeezed out over the conductors, air
being trapped, and hollow spaces being left beneath the conductors.
In contrast to the method of curtain pouring on to cooled printed
circuit boards described in WO 93/14444, it is also possible to
provide structured printed circuit boards having conductive tracks
with a reliable, high-quality coating.
The apparatus according to the invention for coating printed
circuit boards with a coating composition that is crosslinkable by
electromagnetic radiation, especially UV radiation, is a roll
coating apparatus having at least one applicator roll and devices
for applying the coating composition to the applicator roll. It
comprises a melting vessel for a photopolymerisable, meltable,
low-molecular-weight coating composition that is highly viscous to
solid at room temperature and has an average molecular weight of
preferably from 500 to 1500, which melting vessel can be heated and
the temperature of which can be controlled and from which the
molten coating composition is fed to the applicator roll, and also
a device for pre-heating the surface of the printed circuit board
that is to be coated, in which device the surface of the printed
circuit board is pre-heated, prior to coating, to a temperature
that is approximately from 10.degree. to 50.degree. C. higher than
the application temperature of the coating composition, the
temperature of the surface of the printed circuit board not
exceeding a temperature of from 70.degree. to 160.degree. C.
The use of a rubberised applicator roll allows uneven areas of
structured printed circuit boards having conductive tracks to be
better compensated for. The melt resist is largely solventless and
substantially solidifies at room temperature. A heating device
upstream of the roll coating apparatus ensures that the temperature
of the printed circuit board is higher than the application
temperature of the coating composition, but does not exceed
160.degree. C. As a result, the coating composition is not exposed
to relatively high temperatures until it comes into contact with
the printed circuit board, where its viscosity decreases so that it
is able to flow into the smallest spaces and cover all areas
thoroughly. On the other hand, the temperature of the printed
circuit board is not so high that the bonds in the coating
composition are able to decompose. The application viscosity of the
coating composition is, however, sufficiently high that
through-plating holes are covered reliably.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and its associated essential details are described in
greater detail below with reference to the single FIGURE, which
shows a diagrammatic view of a roll coating apparatus according to
the invention.
DESCRIPTION OF THE INVENTION
The process according to the invention is carried out using a roll
coating apparatus. Depending upon the desired type of coating,
one-sided or two-sided, the apparatus may be a single roll coating
apparatus for one-sided coating, or two one-sided roll coating
apparatuses can be connected in series. In the latter case, a
turning station is arranged between the two apparatuses. For the
two-sided coating of printed circuit boards it is, however,
preferred to use a two-sided roll coating apparatus 10, as is shown
by way of example in the single FIGURE. The apparatus shown is in
particular a two-sided roll coating apparatus 10 that is equipped
for the simultaneous coating of both sides of the printed circuit
boards and that has two heatable applicator rolls 1, 3. The
applicator surface of the applicator rolls 1, 3 is preferably
rubberised. The flexibility of the rubber coating is so chosen that
uneven areas of the surface of the printed circuit board, such as
are caused, for example, by conductive tracks having different
heights, can readily be compensated for. Immediately adjacent to
each applicator roll 1, 3 there is arranged a metering roll 2, 4,
which is likewise heatable. The metering rolls are so arranged that
a narrow gap remains between the metering roll 2, 4 and the
respective applicator roll. The width of the gap defines the
thickness of the film of coating composition that forms on the
applicator roll 1, 3. For supplying the coating composition there
is preferably provided above the applicator rolls 1, 3 a heatable
storage container 5 for the coating composition, from which
heat-insulated or heatable supply pipes 6, 7 lead to the respective
pair of rolls 1, 2 and 3, 4. The upper and lower applicator rolls
1, 3 are preferably arranged at a distance from each other that
corresponds approximately to from 50% to 95% of the thickness of
the printed circuit board.
The metering gap between the rubberised applicator rolls 1, 3,
which can be heated to from 60.degree. to 110.degree. C., and the
metering rolls 2, 4, which can be heated to from 70.degree. to
160.degree. C., is so set that a trough of coating composition is
formed between the rolls. The coating composition, which is highly
viscous to solid at room temperature, is liquefied in the storage
container 5 to such an extent that it can be fed to the two pairs
of rolls 1, 2 and 3, 4. For coating, the printed circuit boards L
are transported through the gap between the two applicator rolls 1,
3 at a speed of approximately from 5 to 20 m/minute. Because the
applicator rolls and the metering rolls are heatable, it is
possible to bring the coating composition to the required
application temperature and the required application viscosity only
immediately before it is coated on to the surface of the printed
circuit board. The meltable coating composition that is used
preferably has a softening range of approximately from 20.degree.
to 80.degree. C.
Prior to coating, the printed circuit boards L are brought to the
desired coating temperature in a temperature-control device 8
arranged upstream of the roll coating apparatus 10. In particular,
the printed circuit boards L are so heated in a temperature-control
device 8, prior to coating, that the temperature of their surface
is from 10.degree. to 50.degree. C. higher than the temperature of
the coating composition applied. In this manner, the coating
composition is liquefied even further on the surface of the printed
circuit board in order better to compensate for any uneven areas.
The application viscosity of the coating composition is
approximately from 1000 to 20000 mPas, preferably approximately
from 8000 to 12000 mPas. The relatively high application viscosity
of the coating composition ensures that through-plating holes are
covered thoroughly with coating composition. The temperature of the
surface of the printed circuit boards is so set that the viscosity
of the coating composition over the drill holes is decreased only
to such a degree that the coating composition is unable to flow
away and coverage is maintained.
In a tempering station 9 arranged downstream of the roll coating
apparatus 10, the coated printed circuit boards L are tempered, if
necessary, in order to achieve a non-tacky surface. However, an
exposure station may also be arranged downstream, in which the
coated surface of the printed circuit boards is exposed to UV
radiation for a short time in order to achieve pre-crosslinking at
the surface and thus obtain a non-tacky surface. A combination of a
tempering station 9 and an exposure station is also possible.
The coating can be used as an etching or electro resist that is
removed again after the corresponding treatment of the printed
circuit boards. It may, however, also be used as a permanent resist
for additive processes, as a solder mask or as a mask for the
production of high solder deposits.
The invention is to be described in greater detail by means of the
following Examples. For the preparation of the various exemplary
coating compositions, the following resin components are used:
Resin component A: A resin that is crosslinkable by means of
radiation, is solid at room temperature and has an average
molecular weight of 860, a softening range of from 30.degree. to
40.degree. C. and a viscosity at 70.degree. C. of from 10000 to
20000 mPa.s, obtained by reacting 1 equivalent of a diglycidyl
ether of bisphenol A having a molecular weight of from 188 to 220
with 1.1 equivalents of acrylic acid and then reacting the
resulting product with 0.8 equivalents of hexahydrophthalic acid
anhydride, the reaction being carried out for 3 hours at 80.degree.
C.
Resin component B: A resin that is crosslinkable by means of
radiation, is heat-curable, is solid at room temperature and has a
softening point of from 20.degree. to 30.degree. C. and a viscosity
at 80.degree. C. of from 2000 to 5000 mPa.s. The resin is obtained
by reacting 1 mol of a triglycidyl ether of cresol novolak having a
molecular weight of approximately 580 with 1 mol of acrylic
acid.
Resin component B1: A resin that is crosslinkable by radiation,
obtained by reacting the above-described resin component B for 3
hours at 60.degree. C. with an unsaturated isocyanato carbamate
ester having a molecular weight of 290, which has been obtained by
reacting 1 mol of toluylene-2,4- and -2,6-diisocyanate isomeric
mixture with 1 mol of hydroxyethyl acrylate in accordance with
EP-A-0 194 360, Example 2. Resin component B1 has a molecular
weight of 950, an epoxide equivalent of 475 and a viscosity of
200000 mpa.s at room temperature and from 500 to 1000 mPa.s at
70.degree. C.
Resin component C: Cresol novolak containing flow agent and a
photoinitiator and having a molecular weight of 534, with the
following composition:
60 parts by weight of cresol novolak having a molecular weight of
460,
30 parts by weight of 2-ethylanthraquinone,
5 parts by weight of savinyl blue, and
5 parts by weight of flow agent Byk.RTM.361.
Resin component D: Cresol novolak containing flow agent,
photoinitiator and curing accelerator and having a molecular weight
of 534, with the following composition:
50 parts by weight of cresol novolak having a molecular weight of
460,
10 parts by weight of 2-methylimidazole,
30 parts by weight of 2-ethylanthraquinone,
5 parts by weight of heliofast green, and
5 parts by weight of flow agent Byk.RTM.361.
EXAMPLE 1
An etching or electro resist is to be coated on to the surface(s)
of printed circuit boards.
______________________________________ Printed circuit board: base
material FR 4, thickness: 1.6 mm copper cladding: 17.5 .mu.m
temperature: 120.degree. C. Coating composition 1: 64 parts by
weight of resin component A, 32 parts by weight of resin component
B1, 3 parts by weight of 2-ethylanthraquinone, 0.5 part by weight
of flow agent Byk .RTM.361, and 0.5 part by weight of savinyl blue.
______________________________________
To produce an etching resist or an electro resist, coating
composition 1 is coated on to the printed circuit boards using a
roll coating apparatus.
Applicator roll temperature: 80.degree. C.
Application viscosity of coating composition 1: 1000 mPas
Coating thickness in the case of etching resist: 10 .mu.m
Transport speed of the printed circuit board during coating: 20
m/minute
Coating thickness in the case of electro resist: 40 .mu.m
Transport speed of the printed circuit board during coating: 10
m/minute
The coated printed circuit board is tempered in a vertical position
for 3 to 10 minutes at a temperature of 110.degree.-120.degree. C.
During that time, the components of the coating undergo
pre-crosslinking and produce a non-tacky surface after the printed
circuit board has cooled to room temperature.
EXAMPLE 2
Using the two-sided roll coating process, a coating that is solid
at room temperature is coated on to the surfaces of printed circuit
boards and gives a non-tacky surface after cooling to room
temperature.
______________________________________ Printed circuit board: base
material FR 4, thickness: 1.6 mm copper cladding: 17.5 .mu.m
temperature: 140.degree. C. Coating composition 2: 90 parts by
weight of resin component A, and 10 of resin component C.
______________________________________
The meltable coating composition is applied to produce a non-tacky
etching or electro resist.
Applicator roll temperature: 110.degree. C.
Application viscosity of the coating composition: 1000 mPas
Coating thickness in the case of etching resist: 10 .mu.m
Transport speed of the printed circuit board during coating: 20
m/minute
Coating thickness in the case of electro resist: 40 .mu.m
Transport speed of the printed circuit board during coating: 10
m/minute
The coated printed circuit boards are left in a vertical position
to cool and have a non-tacky surface at room temperature.
EXAMPLE 3
Solder masks in thicknesses of 30 .mu.m and 100 .mu.m are prepared
by applying a meltable coating composition that is solid at room
temperature, using the roll coating process:
______________________________________ Printed circuit board: base
material FR 4, thickness: 1.6 mm conductor height: 60 .mu.m
conductor width: 100 .mu.m conductor spacing: 150 .mu.m
temperature: 90.degree. C. Coating composition 3: 50 parts by
weight of resin component A, 40 parts by weight of resin component
B, and 10 parts by weight of resin component D.
______________________________________
Applicator roll temperature: 70.degree. C.
Application viscosity of coating composition 3: 10000 mPas
Coating thickness: 30 .mu.m
Transport speed of the printed circuit boards during coating: 20
m/minute
Coating thickness: 100 .mu.m
Transport speed of the printed circuit boards during coating: 15
m/minute
After coating, the printed circuit boards cool to room temperature
in a vertical position. Their coated surface is non-tacky at room
temperature.
* * * * *